1. Field of the Invention
This invention relates generally to control devices for road construction and grading vehicles, and relates more particularly to a mounting device for mounting non-contacting sensors to a paver or similar vehicle having a variable-height implement.
2. Description of the Relevant Art
Road construction equipment, such as graders and pavers, have variable-height implements that determine how much earth is graded or how much pavement is laid. A paver, for example, has a variable-height screed that governs the thickness of paving material put down by the paver. When the screed is raised, more paving material is applied. Conversely, when the screed is lowered, less paving material is applied.
It is important to control the height of a variable-height implement in order to obtain the desired graded or paved surface. For a paver, the desired result is a uniform, smooth mat having a specified minimum thickness and being level with any adjacent mats. It is common to use an automatic control system to control the height of a variable-height implement. Such an automatic control system typically takes measurements of the height of the implement as an input, compares the measured height to a reference to determine any positioning error, and adjusts the height of the implement up or down to minimize the error.
Both contacting and non-contacting devices have been used with road construction equipment to measure implement height. An ultrasonic transducer is used in U.S. Pat. No. 4,733,355 to measure the height of a grading implement relative to ground or a stringline. With a paver, it is common to use a contacting device known as a ski to measure the height of the screed. The ski, which is typically 20 to 30 feet long (although it may be longer or shorter), is dragged along the ground or pavement next to the paver, and gives an averaged height of the ground it is traversing. The ski is mechanically linked to the paver and its height is used to control the height of the screed. Some skis have multiple feet or wheels that contact the ground.
Using a ski to control the variable-height screed of a paver has problems, however. The contacting surface of a ski can pick up asphalt or debris that lifts the ski, causing a measurement error. Also, it is difficult to avoid or work around obstacles such as manholes or storm drains when using a ski, or to get accurate readings over rough pavement. Sometimes a ski may interfere with the area to be paved, resulting in gaps that have to be filled in by hand. Using a ski also makes it difficult to maneuver the paver, especially backing up.
It is known to use multiple non-contacting sensors in conjunction with controlling variable-height implements. U.S. Pat. No. 5,258,961, for example, discloses a control unit that includes three sonic sensors mounted to the side of a road surfacing machine or paver as a substitute for a ski. The sensors of the '961 patent are mounted to the paver, without any means disclosed for adjusting their positions relative to the paver.